Table 6.
Explored mechanisms involved in tolerance to different abiotic stresses.
| Mechanism/Traits | Genes/Proteins/Enzymes and Other Molecules Involved | Target Crop | Abiotic Stress | Reference |
|---|---|---|---|---|
| Early flowering | Vernalization (Vrn), photoperiod (Ppd), and earliness per se (Eps) genes; VRN1 and Ppd-D1 | Wheat | Drought | [298] |
| Mutant BW507 line (mutant allele Mat-c) | Barley | Drought | [299] | |
| Osmoprotection and osmotic adjustment | Sugars (glucose, fructose, fructans, and trehalose) | Rice | Salinity | [300] |
| Raffinose family oligosaccharides (RFO) | Rice | Cold and Drought | [301] | |
| γ-aminobutyric acid (GABA) | Wheat | Salinity | [302] | |
| Lignin production (cell wall integrity) | GmRD22 (regulates cell wall peroxidases and hence strengthens cell wall integrity under stress conditions) | Soybean and rice | Salt and osmotic stresses |
[303] |
| Scavenging of ROS: Antioxidant Regulation | ||||
| Enzymatic antioxidants: Catalase and pyrroline-carboxylate synthetase (P5CS), and sustained activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) | Chickpea | Salinity | [292] | |
| Non-enzymatic antioxidant compounds: Helicase proteins (e.g., DESD-box helicase and OsSUV3 dual helicase), Ascorbate, Glutathione |
Rice Pea |
Salinity | [304,305,306] | |
| Flash flood tolerance | SUB1A-1 encoding AP2/ERF (ethylene response factors), family transcription factor | Rice | Flood | [307,308] |
| Anaerobic germination |
OsTPP7 encoding Trehalose-6-phosphate Phosphatase |
Rice | Flood | [309] |
| Internode elongation under submergence |
SK1 (SNORKEL1), SK2 encoding, AP2/ERF family transcription factor |
Rice | Flood | [294] |
| Internode elongation under submergence | SD1 (OsGA20ox2) encoding, Gibberellin 20-oxidase | Rice | Flood | [310] |
| Leaf hydrophobicity and gas films are conferred by a wax synthesis gene (LGF1); formation of gas films necessary for gas exchange and underwater photosynthesis | Leaf Gas Film 1 (LGF1) |
Rice | Flood | [311] |
| Traits: Dormancy/quiescence during submergence; reduced elongation growth and carbohydrate consumption during submergence | SUB1 | Rice | Flood | [308] |
| Underwater photosynthesis: Leaf gas films to facilitate gas exchange; supply of carbohydrates to roots for survival, regeneration, and growth | LGF1/OsHSD1 | Rice | Flood | [311,312] |
| Chlorophyll retention under submergence: Blocking ethylene responsiveness; scavenging reactive oxygen species (ROS) to protect chlorophyll and other cellular membranes | SUB1 | Rice | Flood | [313] |
| Chlorophyll retention under submergence: Scavenging reactive oxygen species (ROS) to protect chlorophyll and other cellular membranes | Several scavengers induced during submergence | Rice | Flood | [313,314] |
| A barrier to radial oxygen loss (ROL): Minimize oxygen losses in the basal portion of the roots and maximize its delivery to the root apex; minimize uptake of toxins generated in anoxic soils |
Rice | Flood | [315,316] | |
| Ion Homeostasis: The excess salt is either transported to the vacuole or sequestered in older tissues which eventually are sacrificed, thereby protecting the plant from salinity stress | SOS1, SOS2, and SOS3 proteins involved in Salt Overly Sensitive (SOS) signaling pathway; SOS1-regulating Na+ efflux at the cellular level. It also facilitates long-distance transport of Na+ from root to shoot. SOS2 encodes a serine/threonine kinase, and is activated by salt stress elicited Ca+ signals. SOS3 is a myristoylated Ca+ binding protein |
Wheat | Salinity | [317] |
| HKT (histidine kinase transporter) located on the plasma membrane and intracellular/tonoplast-localized NHX- encoding K+ transporters | Rice | Salinity | [318,319] | |
| Polyamines (PA)*: Protect cells from stress-induced damages, membrane integrity, regulation of gene expression for the synthesis of osmotically active solutes, reduction in ROS production, and controlling the accumulation of Na+ and Cl− ions in different organs. * PA is a small, low molecular weight, ubiquitous, polycationic aliphatic molecule that is widely distributed throughout the plant kingdom. |
Diamine putrescine (PUT), triamine spermidine (SPD), and tetra-amine spermine (SPM) | Wheat, barley rice |
Salinity | [320,321] |
| Nitric Oxide: Triggers expression of many redox-regulated genes, preventing lipid oxidation, scavenging superoxide radicals, and formation of peroxynitrite that can be neutralized by other cellular processes; activation of antioxidant enzymes | Sodium nitroprusside (SNP), a NO donor |
Maize | Salinity | [322] |
| Hormone Regulation | ABA: The accumulation of ABA can mitigate the inhibitory effect of salinity on photosynthesis, growth, and translocation of assimilates; ABA is involved in the expression of several salt and water deficit-responsive genes including HVP1 and HVP10 genes, TIP 1 and GLP 1 genes, NCP1 and ZmPIF3 proteins | Rice Wheat Barley Maize |
Salinity and drought | [205,323,324,325,326] |
| Compounds that have hormonal properties such as salicylic acid (SA), jasmonates, and brassinosteroids (BR) | Rice Wheat Legumes |
Salinity and drought | [327,328,329] |